Fuel cell system with improved humidification performance

Abstract

The present invention provides a fuel cell system, which reduces the temperature of exhaust gas discharged from a fuel cell stack to a humidifier to increase the humidity thereof when the fuel cell stack operates at high temperature and high power, and thus improves the humidification performance for air as an oxidant in the humidifier and improves the performance of the fuel cell stack. For this purpose, the present invention provides a fuel cell system in which an intercooler is installed in an exhaust gas pipe, which connects a cathode outlet of the fuel cell stack and the humidifier, to cool the exhaust gas as a water supply source of the humidifier such that the intercooler reduces the temperature of the exhaust gas and, at the same time, increase the humidity thereof, thus improving humidification performance for air as an oxidant in the humidifier.

What is claimed is: 
     
       1. A fuel cell system, comprising:
 a fuel cell stack that receives reactant gases and generate electrical energy; 
 a humidifier to humidify reactant gas supplied to a cathode inlet of the fuel cell stack using exhaust gas discharged from a cathode outlet of the fuel cell stack as a water supply source; 
 an intercooler to cool the exhaust gas as a water supply source of the humidifier, wherein the intercooler is installed in an exhaust gas pipe, which connects the cathode outlet of the fuel cell stack and the humidifier, to reduce the temperature of the exhaust gas and, simultaneously, increase the humidity thereof, to improve humidification performance of the humidifier and wherein the humidifier is installed in a pipe connecting the intercooler and the cathode inlet; 
 a coolant cut-off device to selectively supply and cut off coolant to the intercooler, which is heat-exchanged with the exhaust gas within the intercooler, to the intercooler based on an operation state of the fuel cell stack, wherein the coolant cut-off device includes:
 an operation state detector configured to detect an operation state of the fuel cell system; 
 a controller configured to output a control signal to selectively supply and cut off the coolant based on the operation state of the fuel cell stack detected by the operation state detector; and 
 a cut-off valve installed in a path through which the coolant is supplied to the intercooler, wherein the cut-off valve is configured to selectively supply and cut off the coolant to the intercooler based on the control signal of the controller; and 
 
 a bypass device that bypasses all or a part of the exhaust gas discharged from the fuel cell stack from the exhaust gas pipe to the humidifier based on the operation state of the fuel cell stack such that the exhaust gas does not pass through the intercooler, 
 wherein the bypass device includes: a bypass pipe installed in the exhaust gas pipe and installed to bypass the exhaust gas to control passage of exhaust gas through the intercooler; and a bypass valve that controls the flow of exhaust gas in the path between the intercooler and the bypass pipe based on the control signal of the controller. 
 
     
     
       2. The fuel cells system of  claim 1 , wherein the operation state detector is a temperature sensor installed at a coolant outlet of the fuel cell stack and configured to detect the temperature of the coolant passing through the fuel cell stack and configured to detect the temperature of the coolant passing through the fuel cell stack or a temperature sensor installed at the cathode outlet of the fuel cell stack and configured to detect the temperature of the exhaust gas, and the controller determines that the fuel cell stack operates at high temperature and high power only when a detection value of the temperature sensor exceeds a predetermined reference value and outputs a control signal to supply the coolant. 
     
     
       3. The fuel cell system of  claim 1 , further comprising a supply amount control device configured to control the amount of coolant supplied to the intercooler and heat-exchanged with the exhaust gas based on the operation state of the fuel cell system. 
     
     
       4. The fuel cell system of  claim 3 , wherein the supply amount control device comprises:
 an operation state detector configured to detect an operation state of the fuel cell system; 
 a controller configured to output a control signal to control the amount of coolant supplied based on the operation state of the fuel cell stack detected by the operation state detector; and 
 an opening degree control valve installed in a path through which the coolant is supplied to the intercooler and is configured to control the amount of coolant supplied based on the control signal of the controller. 
 
     
     
       5. The fuel cell system of  claim 4 , wherein the operation state detector is a temperature sensor installed at the coolant outlet of the fuel cell stack and configured to detect the temperature of the coolant passing through the fuel cell stack or a temperature sensor installed at the cathode outlet of the fuel cell stack and configured to detect the temperature of the exhaust gas, and the controller outputs a control signal to control the amount of coolant supplied based on a detection value of the temperature sensor. 
     
     
       6. The fuel cell system of  claim 1 , wherein the operation state detector is a temperature sensor installed at the coolant outlet of the fuel cell stack and configured to detect the temperature of the coolant passing through the fuel cell stack or a temperature sensor installed at the cathode outlet of the fuel cell stack and configured to detect the temperature of the exhaust gas, and the controller outputs a control signal to control the amount of exhaust gas bypassed based on a detection value of the temperature sensor. 
     
     
       7. The fuel cell system of  claim 6 , wherein the controller outputs a control signal that bypasses all exhaust gas through the bypass pipe if the detection value of the temperature sensor is less than a predetermined reference value.